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United States Patent |
5,695,428
|
Yuasa
,   et al.
|
December 9, 1997
|
Method and apparatus for controlling a continuously variable transmission
Abstract
A basic speed change ratio is set on the basis of vehicle speed and
throttle valve opening, and a control target speed change ratio is made to
gradually approach the basic speed change ratio in accordance with a speed
change speed. Feedback control is then carried out so that the actual
speed change ratio coincides with the control target speed change ratio.
When there is an up-shift requirement with a rate of change in throttle
valve opening equal to or less than a predetermined value, and a rate of
change in the basic speed change ratio, which is set on the basis of
operating conditions, equal to or less than a predetermined value, the
speed change speed is faster than at the time of an up-shift requirement
with throttle valve closure.
Inventors:
|
Yuasa; Hiroyuki (Kanagawa-ken, JP);
Kashiwabara; Masuo (Kanagawa-ken, JP)
|
Assignee:
|
Unisia Jecs Corporation (Kanagawa-ken, JP)
|
Appl. No.:
|
523600 |
Filed:
|
September 5, 1995 |
Foreign Application Priority Data
Current U.S. Class: |
477/48; 474/18; 477/46 |
Intern'l Class: |
B60K 041/12; F16H 059/00 |
Field of Search: |
477/45,46,48
474/18
|
References Cited
U.S. Patent Documents
4747325 | May., 1988 | Morimoto | 477/46.
|
4753133 | Jun., 1988 | Itoh et al. | 477/46.
|
4827803 | May., 1989 | Miyawaki | 477/46.
|
4831898 | May., 1989 | Miyawaki | 477/46.
|
5009129 | Apr., 1991 | Morimoto et al. | 477/46.
|
Foreign Patent Documents |
62-149526 | Jul., 1987 | JP.
| |
Primary Examiner: Marmor; Charles A.
Assistant Examiner: Rodriguez; Saul J.
Attorney, Agent or Firm: Lowe, Price, LeBlanc & Becker
Claims
What is claimed is:
1. An apparatus for controlling a continuously variable transmission,
wherein a speed change ratio is controlled so that an actual speed change
ratio gradually approaches a basic speed change ratio set in accordance
with operating conditions which include at least throttle opening, said
apparatus comprising:
up-shift requirement judgment means for judging between an up-shift
requirement in a first condition in which a throttle valve opening is
approximately constant and an up-shift requirement in a second condition
in which there is a decrease in the throttle valve opening;
speed change speed switching means for switching a speed change speed based
on the judgment result from said up-shift requirement judgment means; and
speed change control means for changing the speed change ratio of the
continuously variable transmission in accordance with the speed change
speed set by said speed change speed switching means so as to approach
said basic speed change ratio.
2. The apparatus for controlling a continuously variable transmission
according to claim 1, wherein:
said speed change speed switching means sets the speed change speed at the
time of said up-shift requirement in said first condition to be faster
than the speed change speed in the second condition.
3. The apparatus for controlling a continuously variable transmission
according to claim 1, wherein:
said up-shift requirement judgment means judges an up-shift requirement
with an absolute value of a rate of change in throttle valve opening less
than a predetermined value, and an absolute value of a rate of change in
said basic speed change ratio less than a predetermined value, as said
first condition up-shift requirement.
4. The apparatus for controlling a continuously variable transmission
according to claim 1, wherein:
said up-shift requirement judgment means judges the up-shift requirement
based on a comparison between the actual speed change ratio and a basic
speed change ratio set on the basis of vehicle speed and throttle valve
opening.
5. A method of controlling a continuously variable transmission, wherein:
a speed change ratio is controlled so that an actual speed change ratio
gradually approaches a basic speed change ratio set in accordance with
operating conditions which includes at least throttle opening, said method
comprising the steps of:
judging between an up-shift requirement in a first condition in which a
throttle valve opening is approximately constant, and an up-shift
requirement in a second condition in which there is a decrease in the
throttle valve opening;
switching a speed change speed based on said judgment result; and
changing the speed change ratio of the continuously variable transmission
in accordance with said switched speed change speed so as to approach said
basic speed change ratio.
6. The method of controlling a continuously variable transmission according
to claim 5, wherein:
the speed change speed at the time of said up-shift requirement in said
first condition is set faster than the speed change speed at the time of
said up-shift requirement in said second condition.
7. The method of controlling a continuously variable transmission according
to claim 5, wherein:
an up-shift requirement with an absolute value of a rate of change in
throttle valve opening less than a predetermined value, and an absolute
value of a rate of change in said basic speed change ratio equal to or
less than a predetermined value, is judged as said up-shift requirement
with approximately constant throttle valve opening.
8. The method of controlling a continuously variable transmission according
to claim 5, wherein:
the up-shift requirement is judged based on a comparison between the actual
speed change ratio and a basic speed change ratio set on the basis of
vehicle speed and throttle valve opening.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and apparatus for controlling a
continuously variable transmission, and in particular to techniques for
making speed change speeds in a continuously variable transmission
appropriate.
2. Description of the Related Art
It is known with continuously variable transmissions that if the speed
change speed is too fast, the driver will experience a different
sensation. In this respect, a method to appropriately control speed change
speed is disclosed for example in Japanese Unexamined Patent Publication
No. 62-149526.
With this method the speed change speed is determined based on the
deviation of the actual speed change ratio from a target speed change
ratio which is set in accordance with vehicle speed and throttle opening,
and on correction values which are set in accordance with the throttle
opening speeds required to meet acceleration requirements.
More specifically, with up-shift control in a continuously variable
transmission, there is up-shift which is carried out at the time of
throttle valve closure on removal of the foot from the accelerator pedal
(referred to hereunder as foot removal up-shift), and up-shift with an
increase in vehicle speed under approximately constant pressing of the
accelerator pedal (approximately constant throttle valve opening), which
occurs after pressing the accelerator pedal for acceleration (referred to
hereunder as auto up-shift).
In general, the speed change speed requirements for auto up-shift and for
foot removal up-shift are different. At the time of auto up-shift, a
comparatively fast speed change speed is required to avoid a sensation of
a surge in rotation with the slow speed change ratio convergence. On the
other hand, at the time of foot removal up-shift, the speed change ratio
convergence is comparatively fast since the required speed change ratio
for the operating conditions changes gradually in an opposite direction
with the drop in vehicle speed after the temporary sudden speed change
with throttle closure. A comparatively slow speed change speed is
therefore required to avoid a jump sensation.
With the conventional control however, with correction for throttle opening
speed, the correction value for the throttle opening speed is determined
without making a distinction between down-shift and up-shift. Moreover, a
distinction is not made between the abovementioned auto up-shift and foot
removal up-shift, and basically, at the time of a sudden acceleration
requirement, a correction for the throttle opening speed is made to speed
up the down-shift speed change speed. It is therefore not possible to meet
the different requirements in speed change speed with auto up-shift, and
foot removal up-shift, so that at the time of the up-shift, there is the
likelihood of the sensation of a surge in rotation, or a jump.
SUMMARY OF THE INVENTION
The present invention takes into consideration the abovementioned problems,
with the object of controlling the speed change ratio of a continuously
variable transmission at appropriate speed change speeds for auto up-shift
and foot removal up-shift.
Accordingly, the method and apparatus according to the present invention
for controlling a continuously variable transmission wherein a speed
change ratio is controlled so that an actual speed change ratio gradually
approaches a basic speed change ratio set in accordance with operating
conditions which include at least throttle opening, includes judging an
up-shift requirement with approximately constant throttle valve opening,
and an up-shift requirement with a change in throttle valve opening,
switching a speed change speed based on the judgment result, and changing
the speed change ratio of the continuously variable transmission in
accordance with the switched speed change speed so as to approach the
basic speed change ratio.
With such a construction, even though it may be time of the up-shift
requirement, it is judged if this is an up-shift requirement with
approximately constant throttle valve opening, or an up-shift requirement
with a change in throttle valve opening, and the speed change speed is
switched based on the judgment result. Accordingly, different speed change
speeds can be set for the two types of up-shift requirements, enabling
speed change control to be carried out at the appropriate speed change
speed.
The speed change speed at the time of the up-shift requirement with
approximately constant throttle valve opening, may be set faster than the
speed change speed at the time of the up-shift requirement with a change
in throttle valve opening.
With such a construction wherein the speed change speed at the time of the
up-shift requirement with approximately constant throttle valve opening is
set faster than that at the time of the up-shift requirement with a change
in throttle valve opening, convergence on the required speed change ratio
can be ensured at time of the up-shift requirement with approximately
constant throttle valve opening. Moreover, since the speed change speed at
the time of an up-shift requirement with a change in throttle valve
opening is made smaller, there is no sensation of a jump.
Furthermore, an up-shift requirement with a rate of change in throttle
valve opening equal to or less than a predetermined value, and a rate of
change in the basic speed change ratio equal to or less than a
predetermined value, may be judged as the up-shift requirement with
approximately constant throttle valve opening.
With such a construction, since the convergence of the actual speed change
ratio (or the control target speed change ratio) on the basic speed change
ratio is slow, when a comparatively fast speed change speed is required,
control can be made at a speed change speed which meets the requirement.
Here the construction may includee setting a target inertial torque TTINR
based on judgment results of an up-shift requirement with approximately
constant throttle valve opening, and an up-shift requirement with a change
in throttle valve opening, and setting a speed change speed SV based on;
the target inertial torque TTINR, a speed change ratio i, engine inertial
torque I.sub.E, and engine output shaft rotational speed No as;
SV=TTINR/(i.times.I.sub.E .times.No).
With such a construction, even though the speed change ratio range may be
the same, the speed change speed can be changed with output shaft
rotational speed No, so that in particular on the high vehicle speed side,
the speed change speed can be made slower. Therefore inertial torque at
the time of speed change can be kept constant.
Moreover, the construction may include judging the up-shift requirement
based on a comparison between the actual speed change ratio and a basic
speed change ratio set on the basis of vehicle speed and throttle valve
opening.
With such a construction, it is possible to reliably judge the up-shift
requirement on the basis of the intentions of the driver.
Furthermore, the construction may involve feedback control of the speed
change ratio of the continuously variable transmission so that a control
target speed change ratio for the set speed change speed approaches the
basic speed change ratio, and so that the actual speed change ratio
coincides with the control target speed change ratio.
With such a construction, the actual speed change is changed smoothly, even
with sudden changes in the basic speed change ratio, thereby improving
drivability.
Further objects and aspects of the present invention will become apparent
from the following description of embodiments given in conjunction with
the appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing a basic configuration of the present
invention;
FIG. 2 is a schematic system diagram illustrating an embodiment of the
present invention;
FIG. 3 is a flow chart illustrating a speed change speed switching control
routine for the embodiment;
FIG. 4A and 4B time charts respectively illustrating control
characteristics of the embodiment during foot removal up-shift and auto
up-shift;
FIG. 5 is a flow chart illustrating a more preferred embodiment of a speed
change speed control routine; and
FIG. 6A and 6B charts time for illustrating problems with conventional
Prior art techniques.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
As follows is a description of embodiments of the present invention.
FIG. 2 shows a schematic system diagram of an embodiment of the present
invention.
In FIG. 2, a continuously variable transmission for vehicle 1 fitted to an
engine (not shown in the figure), comprises a primary pulley 2 on the
engine side, a secondary pulley 3 on the drive shaft (differential) side
and a belt 4 connected therebetween. With the continuously variable
transmission 1, the speed change ratio can be changed continuously
variably by adjusting speed change pressure to an actuator 2a on the
primary pulley side, and line pressure to an actuator 3a on the secondary
pulley side to thereby change the pulley ratio. Other configurations for
the continuously variable transmission such as a toroidal type
continuously variable transmission are also possible.
The speed change pressure and the line pressure are adjusted by controlling
solenoid valves 7, 8 which function to relieve the oil pressure in a
hydraulic circuit 6 connected to an oil pump 5. The solenoid valves 7, 8
are controlled by means of a controller 9.
The speed change ratio can thus be continuously variablely controlled, by
controlling the solenoid valves 7, 8 with the controller 9 to thereby
adjust the speed change pressure and line pressure.
With the present embodiment, speed change ratio and torque ratio are
defined as;
##EQU1##
To control the speed change ratio, respective detection signals are input
to the controller 9 from: a vehicle speed sensor 10 which detects vehicle
speed VSP, a throttle sensor 11 which detects the throttle opening TVO,
and an engine rotation sensor 12 which detects the engine rotational speed
Ne.
The controller 9 uses an internal microcomputer to set a control target
speed change ratio, based on the abovementioned signals, and feedback
controls the solenoid valves 7, 8 so that the actual speed change ratio
coincides with the control target speed change ratio, thereby effecting
speed change control.
More specifically, a required basic speed change ratio is set from
operating conditions which are based on the vehicle speed VSP and throttle
opening TVO. When there is a deviation between the basic speed change
ratio and the control target speed change ratio, the control target speed
change ratio is steppingly changed in predetermined amounts so as to
gradually approach the basic speed change ratio. The solenoid valves 7, 8
are then feedback controlled so that the actual speed change ratio of the
transmission obtained from the engine rotational speed Ne and the vehicle
speed VSP, approaches the control target speed change ratio.
Here the speed change speed is determined by the unit amount that the
control target speed change ratio is steppingly changed towards the basic
speed change ratio.
The control routine for setting the speed change speed which is given as a
step change amount of the control target speed change ratio, will now be
described with reference to the flow chart of FIG. 3.
With the present embodiment, the functions of an up-shift requirement
judgment device, a speed change speed switcher, and a speed change
controller (refer to FIG. 1) are realized by software illustrated by the
flow chart of FIG. 3 and stored in the controller 9.
In the flow chart of FIG. 3, initially in step 1 (with "step" denoted by S
in the figures), it is judged if current conditions are those for up-shift
requirement, or those for down-shift requirement, by comparing the basic
speed change ratio with the control target speed change ratio.
The basic speed change ratio is determined based on the vehicle speed VSP
and the throttle valve opening TVO changes in the up-shift direction
relative to the decreasing change in throttle valve opening or the
increasing change in vehicle speed, and in the down-shift direction
relative to the increasing change in throttle valve opening or the
decreasing change in vehicle speed.
In the case of a down-shift requirement, control proceeds to step 2, where
a speed change speed to suit the down-shift requirement is set.
On the other hand, when judged that there is an up-shift requirement,
control proceeds to step 3 where it is judged if the absolute value of the
change in throttle opening .DELTA.TVO per unit time is equal to or above a
predetermined value.
As is described before, the up-shift requirement is generated relative to
the decreasing change in throttle valve opening or the increasing change
in vehicle speed. Therefore, in the following steps 3 and 5, it is judged
with which changes the up-shift requirement is generated.
When the change in opening with throttle operation is equal to or above the
predetermined value, an up-shift requirement with a change in throttle
valve opening is judged, and control proceeds to step 4 where a speed
change speed to suit the up-shift requirement with a change in throttle
valve opening is set. The basic speed change ratio determined from the
vehicle speed VSP and throttle opening TVO, is generally set with the
throttle closure direction in the up-shift direction. Therefore the
up-shift requirement with a change in throttle valve opening, is an
up-shift requirement with closure of the throttle as occurs with foot
removal from the accelerator pedal, an operating condition that is
referred to hereunder as foot removal up-shift.
The foot removal up-shift is this an operating condition in which there is
a sudden change in the basic speed change ratio due to closure of the
throttle, i.e. as the throttle valve opening changes towards its fully
closed state as the operator's foot is removed from the accelerator pedal
and is followed by a gradual change in the basic speed change ratio in the
opposite direction with the subsequent drop in the vehicle speed VSP.
Accordingly, the subsequent basic speed change ratio exhibits a change
towards the control target speed change ratio, in spite of the large
deviation of the basic speed change ratio from the control target speed
change ratio with throttle closure (refer to FIG. 6). Therefore, the
requirement for speed change speed adjustment, is minimal, and if the
speed change speed is excessively fast, then a jump sensation is
experienced by the driver.
Accordingly, in step, 4, a slow speed change speed (small step change
amount) is given compared to at the time of auto up-shift (to be described
later), so that the control target speed ratio (actual speed change ratio)
approaches the basic speed change ratio at a sufficiently slow speed.
On the other hand, when in step 3, the change in throttle opening is judged
to be small, control proceeds to step 5 where it is judged whether or not
the absolute value of the change rate of the basic speed change ratio is
less than a predetermined value. When the change rate of the basic speed
change ratio is judged to be less than the predetermined value, there is
assumed to be an up-shift requirement, produced by a gradual change in the
basic speed change ratio with increasing vehicle speed VSP under
conditions wherein changes in throttle opening are sufficiently small
(with this embodiment the up-shift is referred to as auto up-shift). In
this case, control proceeds to step 6 where a speed change speed to suit
the auto up-shift is set.
At the time of auto up-shift, since the basic speed change ratio gradually
changes in accordance with the increase in vehicle speed VSP, then if the
speed change speed at the time of changing the control target speed change
ratio to approach the basic speed change ratio is small, convergence on
the basic speed change ratio will be poor, giving the sensation of a surge
in rotation (refer to FIG. 6). Accordingly in step 6, a fast speed change
speed (large step change amount) is given compared to at the time of the
foot removal up-shift requirement, to give a rapid convergence on the
basic speed change ratio.
Once the speed change speed (step change amount for the control target
speed change ratio) has been set based on the judgment of foot removal
up-shift, auto up-shift, or down shift, then in step 7, the control target
speed change ratio is set so as to gradually approach the basic speed
change ratio in accordance with the speed change speed. Then feedback
control is carried out so that the actual speed change ratio coincides
with the control target speed change ratio.
In this way, even though the up-shift requirement may be the same, it is
judged if this is a foot removal up-shift requirement, or an auto up-shift
requirement, and since the speed change speed for an auto up-shift
requirement is made faster than that for a foot removal up-shift
requirement, then speed change ratio convergence at the time of auto
up-shift can be ensured. As a result, the sensation of a surge in rotation
given to the driver at the time of auto up-shift can be avoided, and there
is also no sensation of a jump at the time of foot removal up-shift (refer
to FIG. 4).
A description of a more preferred embodiment for speed change speed control
by means of the above mentioned auto up-shift and foot removal up-shift
judgment, will now be described with reference to FIG. 5.
In step 11 in the flow chart of FIG. 5, the required basic speed change
ratio is obtained from operating conditions based on vehicle speed VSP and
throttle opening TVO.
In step 12, the rotational speed No of the transmission output shaft is
detected. This detection can be made using the vehicle speed sensor.
Then in step 13, the actual speed change ratio is detected. Since the
actual speed change ratio can be obtained from the engine rotational speed
Ne (transmission input shaft rotational speed) and the transmission output
shaft rotational speed No, then it is computed from these.
›46!
In step 14, it is judged if speed change control is for foot removal
up-shift, auto up-shift, or down shift, as shown by the flow chart of FIG.
3.
Depending on the judgment of step 14, control proceeds to step 15, 16 or
17, to compute a target inertial torque corresponding to the shift type.
In the case of the continuously variable transmission, when the speed
change speed at the time of speed change is large, the generation of
negative inertial torque produces a sensation of speed reduction
(hesitation) at the time of down-shift, and the sensation of a jump at the
time of up-shift. Therefore the target inertial torque is set so as to
control the inertial torque at the time of speed change, to a target value
corresponding to operating conditions.
The target inertial torque is preferably increasingly set in accordance
with for example an increase in engine torque. Moreover, with the present
embodiment, even though the engine torque may be the same, the target
inertial torque at the time of auto up-shift is made a maximum, and at the
time of foot removal up-shift is made a minimum, while at the time of down
shift it is set to an intermediate value.
The engine torque can be estimated on the basis of the throttle valve
opening TVO and the engine rotational speed Ne. Moreover, the method of
setting the target inertial torque is not limited to the abovementioned
method, and may involve a construction wherein the target inertial torque
is set based for example on; deviation of the actual speed change ratio
from the basic speed change ratio, deviation of the current vehicle drive
force from the vehicle drive force when controlled to the basic speed
change ratio, a rate of change of the basic speed change ratio, a rate of
change of the vehicle drive force, or other parameters. Moreover the
construction may be such that the target inertial torque set by these
various setting methods is at least set larger at the time of auto
up-shift than at the time of foot removal up-shift.
Once the target inertial torque has been set in accordance with the
operating conditions and the shift classification, then in the next step
18, a step change amount SV corresponding to speed change speed used at
the time of changing the control target speed change ratio is set based
on; the actual speed change ratio i obtained in step 13, the transmission
output shaft rotational speed No obtained in step 12, the target inertial
torque TTINR, and the engine inertial torque I.sub.E given as a constant,
according to the following equation;
SV=TTINR/(i.times.I.sub.E .times.No).
According to the above equation, when the target inertial torque is larger,
the step change amount, in other words the speed change speed, is set
faster. As a result, the speed change speed at the time of auto up-shift
can be set faster than that at the time of foot removal up-shift.
Moreover, according to the above equation, even though the speed change
ratio range may be the same, the speed change speed changes with the
vehicle speed (output shaft rotational speed No), and in particular the
speed change speed on the high vehicle speed side becomes slower.
Therefore inertial torque at the time of speed change can be kept
constant.
Once the step change amount which determines the speed change speed has
been computed, control proceeds to step 19 where the basic speed change
ratio and the control target speed change ratio are compared.
When the control target speed change ratio is greater than the basic speed
change ratio, control proceeds to step 20 where the control target speed
change ratio is reducing set by the step change amount SV. On the other
hand, when the control target speed change ratio is less than the basic
speed change ratio, control proceeds to step 21 where the control target
speed change ratio is increasingly set by the step change amount SV. The
control target speed change ratio thus gradually approaches the basic
speed change ratio in accordance with the step change amount SV.
Then, in step 22, feedback control is carried out so that the actual speed
change ratio coincides with the control target speed change ratio.
Although the present invention has been described and illustrated in
detail, it should be clearly understood that the same is by way of
illustration and example only and is not to be taken by way of limitation,
the spirit and scope of the present invention being limited only by the
terms of the appended claims.
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